As demands for higher speed, higher power circuits increase, the need for devices having faster switching speeds, higher current carrying capability and increased reverse bias breakdown voltages has also increased. Applications such as power modules for motor and generator control, electronic ballasts for lighting control, industrial robots, display drivers, automotive ignition and automation control would all benefit from higher power, higher speed switches. Unfortunately, existing implementations of higher speed power MOSFETs, IGBTs or MOS controlled thyristors have had limited success in creating devices with very high reverse bias breakdown voltage, a low leakage current, low forward on-state resistance and a high switching speed. Field controlled thyristors have been investigated as high power devices but these devices were limited in their switching speeds. Further development is required to produce a high power, high current device with high switching speeds.
The field controlled bipolar switch is a three terminal device where a P-i-N rectifier structure has a gate structure introduced to control the current flow between the anode and cathode terminals. Because these devices can operate under a high level of injected minority carriers in the drift region, field controlled thyristors operate at very high current densities with a low forward voltage drop. Unfortunately, because of the high level of injected minority carriers, field controlled thyristors were incapable of operating at high frequencies. In fact, the stored minority carriers in the drift region has limited the switching speed of previous devices to below 1 Mhz. In fact, the typical forced gate turn off times for existing field controlled thyristors are between 1 to 20 .mu.secs depending upon the designed breakdown voltage of the device and gating techniques. Baliga, B. J., Modern Power Devices, 1987, pp. 196-260.
Recently issued U.S. Pat. No. 5,387,805 to Metzler et al. describes a field controlled thyristor where the current path from the anode to the cathode passes through a channel region adjacent a void in the channel layer. The device pinches off the current through utilization of p-type regions which surround the void. This device, however, is limited to current densities below 400 A/cm.sup.2 and has a voltage blocking gain of 150 and is limited to gate voltages of 2 to 10 volts. Thus, the maximum theoretical anode voltage attainable by the device would be 1500 volts. Metzler et al. also describes various other patents which relate to field controlled devices. However, as described by Metzler et al., none of these patents describe devices having the characteristics of the devices of the present invention.
For example, U.S. Pat. No. 4,937,644 to Baliga describes an asymmetrical field controlled thyristor. The Baliga patent describes a device which has a DC blocking gain of greater than 60 and claims improved switching speed but provides no data on the switching speed of the device. This device is limited to forward blocking voltages of up to about 2000 volts.
Therefore, there remains a need to develop high performance field controlled devices which exhibit higher breakdown voltages, low on state resistance, higher current capabilities and higher switching speeds.